1. Field of the Invention
The present invention generally relates to lid locking mechanisms for a cassette and, more particularly, is directed to a lid locking mechanism for a tape cassette which locks a lid for closing and opening the front face of a magnetic tape at a closed position.
2. Description of the Prior Art
A tape cassette has been proposed, in which tape reels for winding therearound a tape-shaped recording medium are rotatably accommodated in a box-shaped cassette casing which is formed by combining two cassette halves or cassette shells, the recording medium is extended outward along the front wall of the cassette casing between tape outlets formed at both end portions of a front wall of the cassette casing, and a lid for opening and closing a front surface of the recording medium which extends along the front wall of the cassette casing is supported at a front portion of the cassette casing so as to become rotatable upward and downward. This type of tape cassette is usually provided with a lid locking mechanism for locking the lid at a closed position wherein the front face of the recording medium (magnetic tape) disposed along the front face of the cassette casing is covered or closed by the lid.
An example of the conventional lid locking mechanism will be explained with reference to FIGS. 1 to 3.
Referring to FIGS. 1 to 3, each of an upper half a and a lower half b is formed by molding synthetic resin.
A cassette compartment c is formed on one of opposite end portions of the front edge of a bottom wall d of the lower half b. The cassette compartment c has an elongated rectangular configuration along the side wall of the lower half and its front end is notched to form a slit e. Two recesses f, f are formed at both sides of the top end of the cassette compartment c. Further, top and bottom ends of the cassette compartment c are opened.
A guide groove g is formed on the bottom surface of the bottom wall d of the lower half b at portion corresponding to the bottom portion of the cassette compartment c.
A lid locking member h of an elongated hook-like configuration is provided at a top end thereof with supporting pins i, i of short cylindrical configuration which projects outwardly from the opposite sides thereof.
The lid locking member h is further provided with a groove j opened to the rear end thereof which is positioned at a portion of one of the opposite sides of the top end thereof and along a proximal end of the supporting pin i. Spring engagements k, k are projected at upper and lower opening ends of the groove j.
A portion of the lid locking member k positioned on a front face thereof slightly above the center portion thereof projects forwardly to form a projection l. Further, a portion of the lid locking member h positioned at the bottom end of the front face projects forwardly to form a pressed portion m.
Thus constituted lid locking member h is inserted within the cassette compartment c in a manner that the supporting pins i, i are positioned in the recesses f, f of the accommodating portion c.
At two portions on the lower surface of a top wall or ceiling n of the upper half b, pressing elements o, o project downwardly from the lower surface thereof parallel and opposite with each other in the horizontal direction. When the upper and lower halves a and b are coupled, the lower surfaces of the pressing elements o, o abut the top ends of the both side walls of the accommodating portion c respectively, thereby closing the upper openings of the notches f, f which receives the supporting pins i, i of the lid locking member h, so that the supporting pins i, i are prevented from being dropped out from the notches f, f.
The coil portion of a torsion spring p is wound round one of the supporting pins i so as to be positioned in the groove j. One of the arms of the torsion spring p is resiliently abutted against the lower surface of the top wall of the upper half a and the other arm is resiliently abutted against the lower surface of the groove j, so that the lid locking member h is resiliently biased such that its bottom end turns forwardly.
Thus, when the lid locking member h is not applied with a pressure from its front side, a portion of the front face thereof just above the pressed portion m abuts against the front edge of the bottom opening of the cassette compartment c, and so the lid locking member h is prevented from turning forwardly any more. A position of the lid locking member h in this state is called a locked position. In this state, the pressed portion m is positioned in the guide groove g of the cassette casing.
A front lid r is rotatably supported at the front edge of the cassette casing. As shown in FIGS. 2 and 3, a portion of the inner surface of the front wall of the front lid r positioned slightly below the projection l of the lid locking member h is projected rearwardly to form an engagement portion s.
In the closed position of the front lid r in which the front portion of the cassette casing is closed by the front lid r, the projection l of the lid locking member h is positioned just above the engagement portion s of the front lid r.
In this state, even if the force is applied to the front lid r so as to forcibly turn it towards the open position, the front lid r is prevented from being turned since the engagement portion s engages with the projection l of the lid locking member h.
When the tape cassette having the thus constituted lid locking mechanism is loaded in a recording and/or reproducing apparatus, a locking releaser provided in a cassette holder (not shown) of the recording and/or reproducing apparatus is inserted into the guide groove g to press the pressed portion m of the lid locking member h rearwardly. Then, the lid locking member h turns rearwardly against the resilient force of the torsion spring p such that the bottom end thereof moves rearwardly. Thus, since the projection l moves rearwardly from the position just above the engagement portion s of the front lid r, the front lid r becomes free to turn towards its open position.
Therefore, the locking of the front lid r by the lid locking member h is released.
However, the thus constituted lid locking mechanism for a tape cassette has the disadvantage such that when the force is applied to the front lid r so as to forcibly turn it towards the open position, an abutment between the upper and lower halves a and b opens.
When the force is applied to the front lid r so as to forcibly turn it towards the open position, the engagement portion s of the front lid r tends to move upwardly while turning. However, since the projection l of the lid locking member h is positioned just above the engagement portion s, the engagement portion s abuts against the projection l and so it can not move upwardly any more. Thus, the front lid r can not turn upwardly towards the open position.
If any more force is applied to the front lid r so as to forcibly turn it towards the open position, the force is applied to the lid locking member h so as to lift it upward, and so the force is further applied through the supporting pins i, i of the lid locking member h to the portion of the upper half a where the pressing elements o, o are formed so as to lift it above. The abutment between the upper and lower halves a and b is not fixedly combined but detachably connected with each other by screws or the like at several portions. Thus, if the above-described force is applied to the upper half a through the lid locking member h, a part of the upper half a is detached or separated from the lower half b, so that an operator may feel uneasiness. Further, when the force for forcibly turning the front lid r upwardly is large, the abutment between the upper and lower halves a and b coupled by the screws or the like may be broken due to the stress concentrically applied thereto.